This invention relates to a wire rope, in particular, to a wire rope having an independent wire rope core (hereinafter referred to as "core rope") and suitable for a running rope.
Running ropes require both a high strength and a high flexibility. For such running ropes, generally, the so-called IWRC wire ropes have been used. The IWRC wire rope uses an Independent Wire Rope Core (IWRC) into which a given number of strands are closed.
It should be noted that in this specification, the verb "strand" means to twist together a number of wires into a strand, and the verb "close" means to twist together a number of strands into a wire rope.
FIGS. 5A to 5D show a construction of a typical IWRC wire rope or IWRC 6.times.Fi(25) JIS Type-14. This IWRC wire rope includes a core rope 11 and six outer strands 14. Each outer strand 14 includes a center wire, six intermediate wires, six filler wires, and twelve outer wires. As shown in FIG. 5A, specifically, the core rope 11 is formed by closing seven strands 12 each having seven stranded wires 13. The six outer strands 14 are closed on the core rope 11. Such IWRC wire rope is used as a running rope for use in construction machines, cranes, well drilling machines, and the like.
In the conventional IWRC wire ropes, however, there have been the following problems. Outer strands 14 and the core rope 11 are likely to rub each other when being placed in operation, ausing wires of outer strands 14 or the core rope 11 to be worn out or bent, finally resulting in breakage of wires. Also, when a high pulling force or other external force is applied to the wire rope, strands 12 of the core rope 11 or wires 13 of a strand 12 displace one another due to the heavy load, and outer strands 14 move into a space between strands of the core rope 11, resulting in breakage of wires or a deformation of the core rope 11. These problems inevitably decrease the life of the wire rope.
The following can be considered to be causes of these problems. The core rope 11 which is formed by closing seven strands 12 each having seven stranded wires 13, as shown FIG. 5A, has six vertex-like projections and six big recesses in a cross section thereof. As shown in FIGS. 5B and 5D, the outer strands 14 closed on the core rope 11 are in point contact with the core rope 11. The vertex-like projection or the outermost wire 13 of the strand 12 receives the heaviest load when the heavy load is applied to the wire rope. Further, the core rope 11 has the biggest recesses in the outer periphery thereof. Accordingly, the strands 12 and wires 13 displace one another due to the heavy load, and outer strands 14 are consequently likely to move into recesses between strands 12 as shown in FIG. 5C. Also, as the strands 12 constituting the core rope 11 have generally round sections, and the wires 13 constituting the strand 12 have generally round sections, they are liable to move.
In view of these problems in the conventional IWRC wire ropes, there has been a demand for a novel IWRC wire rope having a high resistance to damages such as breakage of wires and deformation, and having a longer life.